Trani chattering w/tires on & doesn’t move. Tires off & no chatter. Driveshafts aren’t stripped. Spur gear is okay but a couple of clutch pads have broken. Diff gears are fine but the lube was dried up. Pinion mesh is okay. G-son’s truck that I’m trying to help with. I’m guessing the spur assembly, being those clutch pads broken. Also is there a certain weight of grease for the diff ??